Softening Behavior Of Hybrid Laser-arc Welded7075-T6Aluminium Alloys

Hybrid welded Al-Zn-Mg-Cu alloy joints such as7075-T6appears serious "softening"phenomenon after welding, so it’s very important that the effects of porosity on weldstrength of porosity need to be evaluated quantitatively. But for a long time, due to thelimitation of technical conditions and the analysis method, the research can only acquire thestatistical results of rough of porosity. Furthermore some works exist contradictoryconclusions. By using conventional testing methods such as the cross-tensile testing, theOM, the SEM/EDS, the TEM, as well as using high-resolution synchrotron radiationX-rays(SSRF) for the first time, the analysis deeply investigated the softening mechanismof laser-MIG hybrid welded7075-T6aluminium alloys, and a new strength model was thenestablished. To elucidate the physical causes of such strength change, the distribution ofstrengthening elements such as Zn and Cu and the three-dimensional gas porosity weremapped. The interesting findings included the following:(1) Hybrid welds only reach approximately53%of the ultimate tensile strength of theparent phase, and the lowest strength is situated in the central fusion zone.(2) Due to the excessive evaporation of elemental Zn and the significant inversesegregation of elemental Cu in central fusion welds, the major strengthening elementsgather near the heat-affected zone.(3) The elastic modulus of hybrid welds is slightly larger than that of their parentalloys, probably as a result of the in homogeneity in their chemical composition,microstructure, geometry and residual stress.(4) The pore size ranges from below0.01μm to approximately107μm, and it ismodeled by the Schwartz-Saltykov method to reveal its damaging effects on the strength.(5) A strength model of7075-T6butt welded joints is established to correlate with theelastic modulus, porosity and heat inputs, and it coincides well with the computational andexperimental results.(6) The porosity has little influence on the static strength of hybrid welds, and the heatinputs plays the dominant role in defining the static strength of hybrid welds.